Solid freeform fabrication is fast becoming a popular process for manufacturing three-dimensional objects including prototype parts, models, production pieces and working tools. Solid freeform fabrication is a process in which an object, which is described by electronic data, is automatically built from build materials. A principal form of solid freeform fabrication involves a selective deposition process.
When solid freeform fabrication uses a selective deposition process, a number of fabricated planar layers are combined together to form a three-dimensional object. Layers are fabricated by, for example, dispensing or ejecting a binder onto a build material, such as a flat bed of powder or slurry. Where the binder is ejected, the build material is solidified into a cross section of the object being formed. This fabrication is performed layer-by-layer, with each subsequent layer representing a subsequent cross section of the final desired product. Adjacent layers are adhered to one another in predetermined patterns to build up the desired product. Alternatively, freeform fabrication may be performed by selectively ejecting a build material layer-upon-layer to form the desired product.
In addition to selectively forming each layer of the desired object from the build material in the fabrication chamber, the system can apply a color or a color pattern to each layer of the object. For example, inkjet printing technology, such as drop-on-demand technology, can be employed in which a number of differently colored inks are selectively ejected from the nozzles of a dispensing member and blended on the receiving medium to provide a full spectrum of colors. On each individual layer, conventional two-dimensional multi-pass printing techniques and half-toning algorithms can be used to hide dispensing system defects and achieve a broad range of desired color hues.
However, the application of two-dimensional dispensing techniques to three-dimensional solid freeform fabrication fails to properly account for the third dimension and causes several undesirable results. In particular, the multiple dispensing members may become misaligned. This member-to-member misalignment causes vertical roughness along the vertical surfaces of the object being fabricated in a solid freeform fabrication system. In addition to the vertical surface roughness, the member-to-member misalignment results in inaccurate dimensions in the final object. Moreover, when multiple colors are dispensed from different dispensing members, the member-to-member misalignment causes a color-to-color misalignment resulting in color hue shift that is particularly noticeable on vertical surfaces of the fabricated object.